Our aim is to study the distribution of nicotinic acetylcholine receptors in intact and cultured tissues of the peripheral and central nervous system in relationship to the development and function of synapses. To this purpose histochemical localization of alpha-bungarotoxin bound to the receptors is used in conjunction with light and electron microscopy. In the past year we have used an alpha-bungarotoxin-horseradish peroxidase conjugate to identify the synaptic sites of nicotinic acetylcholine receptors in the chicken retina and studied the control of nicotinic acetylcholine receptor aggregation on cultured skeletal muscle cells by neuroblastoma-glioma hybrid cells and by substances secreted by these cells. BIBLIOGRAPHIC REFERENCES: Bender, A. N., Ringel, S. P., Engel, W. K., Vogel, Z. and Daniels, M. P.: Immunoperoxidase localization of alpha-bungarotoxin (alpha BT) binding: A new approach to the study of myasthenia gravis. Ann. N. Y. Acad. Sci. 274: 20-30, 1976. Ringel, S.P., Bender, A.N., Engel, W.K., Daniels, M.P. and Vogel, Z.: A sequential study of denervation-ultrastructural immunoperoxidase localization of alpha-bungarotoxin. Trans. Am. Neurol. Assoc. 100: 52-56, 1975.